Rotational X-ray scans are often used for visualizing a patient's three-dimensional anatomy typically by injecting contrast agents to increase an X-ray attenuation of an organ of interest. Due to a limited field of view, X-ray dose and contrast agent dose saving considerations, a proper iso-centering is a crucial part prior to a rotational scan to avoid double scanning.
In the process of iso-centering in particular the patient's underlying table is moved to center a volume of interest on an iso-center of a frame of an X-ray acquisition device. During an acquisition of X-ray images, the frame assumes a particular stationary position except for a circumferential rotation. For example, an X-ray source attached to the frame faces to an X-ray detector at an opposite side of the frame. In operation, as the X-ray beam traverses the inside of the frame, the beam passes through the iso-center. During a circumferential rotation of the frame around its iso-center, the beam rotates around the iso-center, too. Accordingly, the iso-center corresponds to the intersection of the centers of the angular instances of the beam as it rotates.
Current, iso-centering is done manually by injecting small amounts of contrast agent into the organ of interest and by adjusting a table position, with the patient lying on the table, while acquiring several projections from different viewing directions. The success of such an iso-centering process depends on a plurality of conditions, such as the complete filling especially of distal parts of the organ of interest during the iso-centering process and the ability to acquire lateral projections needed for table height positioning, keeping in mind space constraints due to large patients or equipment.
WO 2008/015612 A2 discloses an automated determination of an optimal table position for rotational angiography, which is performed on the basis of determination of a translation vector pointing from a point of gravity of the object of interest to an iso-center of the examination apparatus. Here, multiple two-dimensional projections are conducted.
US 2002/090058 A1 describes an interventional X-ray system including an X-ray tube and an imaging system which detects emitted X-rays and generates X-ray image data. The X-ray tube and the imaging system are supported by a C arm. A three dimensional (3D) workstation is supplied with the generated X ray image data and volume data pertaining to the same specific portion of the same patient as the X-ray image data. From the volume data, 3D image data may be generated. An operator may, through an input device, designate an interest point on the 3D image data, and subsequently the C arm may be moved so that an iso center of the X-ray system is positioned on or near the interest point.
US 2011/0002444 A1 discloses an interventional X ray system with an X ray source and an imaging unit mounted on a C arm. An interface unit receives image data representing an acquired image of an object from the imaging unit. From the image data, position data of object components, for example organs and/or bones of a patient, is determined; the object components positions may then be matched with position data of components of an anatomical model stored in a memory. In particular, the stored anatomical model is adapted so that a virtual projection of the model fits the acquired X ray image. Based on the matching, an image of the adapted anatomical model is generated and presented to a user. Within this image, a component of interest can be selected, following which a carrier of the object is shifted so that the component of interest is positioned to the center of rotation of the X ray system.